Though surface heat of Earth has stabilised since 1999, studies have found that atmospheric heat continues to rise unabated with the oceans absorbing a large amount of this heat and warming in the past decade (2000-2012).
However, a new study by Sang-Ki Lee of the University of Miami, U.S., and others has found that the Indian Ocean has been warming the most rapidly while the adjoining Pacific Ocean has been getting cooled during the past decade. The study was published in a recent issue of the journalNature Geoscience.
In fact the Indian Ocean accounts for 70 per cent of all the global oceans heat gain up to 700 metres depth during the past decade.
The analysis shows that the abrupt increase of the Indian Ocean Heat Content at 700 metres depth (OHC) during 2003-2012 was not due to surface heating, but rather due almost entirely to horizontal advective heat convergence (caused by winds and resulting currents). Further heat budget analysis indicates that inter-ocean heat transport from the Pacific Ocean to the Indian Ocean via the Indonesian passages was the main cause of the increased Indian OHC; it greatly increased during 2003-2012, overcompensating for the slightly increased southward heat transport from the Indian Ocean to the Southern Ocean.
The study found that the La Nina-like conditions in the Pacific Ocean, caused by a number of La Nina events in the last decade have caused the cooling of the Pacific ocean by transfer of heat to the Indian Ocean, warming the latter.
The La Nina conditions cause strong easterly winds to blow from the western Pacific Ocean and these winds cause currents to flow westward conveying the heat of the Pacific Ocean into the Indian Ocean through what is known as the Indonesian Throughflow (ITF).
The easterlies are formed due to a pressure gradient between the Pacific and Indian Oceans caused by cold conditions in the east and warm wet conditions in the west during a La Nina. Also during a La Nina, the walker circulation — an ocean-atmospheric phenomenon of the Indian Ocean — is strengthened.
The walker circulation leads to abnormally high sea surface temperatures in the western Indian Ocean which in turn leads to copious rainfall in the western Indian Ocean at the cost of the Indian subcontinent and results in a weak monsoon. In contrast to this, as there were relatively much fewer La Ninas in the previous decade (1990-99) there was much less warming in the Indian Ocean.
